This project concerns the development and application of open path (OP) FTIR technology to workplace air monitoring. Such a system could be used for real-time monitoring of almost all gases and vapors, and particularly of labile or polar compounds that could not be monitored easily by conventional methods, does not use sampling pumps, lines or a gas sample cell, and is capable of up to two analyses per second. The development and validation of this OP method is justified by the use of respirators at industrial sites, and to protecting personnel at hazardous waste sites. During the first two years of this NIOSH sponsored project we have addressed the questions of OP-FTIR instrument use under conditions of varying temperature and humidity, under conditions simulating the workplace, and in the workplace. These tests have been directly related to the situation where there is a slowly varying analyte concentration field, and path-averaged beam results were well-correlated with TWA continuous monitor results. In a recent test, the relationship was investigated between detection of a chemical leak at a work station, & signalling the need for an appropriate PPE level. In the first two years of the project we have come to understand that there is a fundamental difference between the OP-FTIR system used in a fixed beam path mode, akin to fixed position area monitors but delivering a spatial average concentration, and a moveable or multiple beam mode, the latter of which is capable of delivering information on spatial distribution of contaminants in the work space. We have explored, both theoretically and experimentally, the fixed beam application. To identify and exploit the particular advantages of OP-FTIR are the purposes of this research. This will be accomplished through performing chamber and field trials to verify the suitability of the fixed and moveable/multiple beam geometries of the OP-FTIR in establishing upper limits on personal exposure and to detect departures from standard operating conditions, with special reference paid to the time-rate-of-change of the concentration field.